1. Field of Invention
The invention relates to the field of gear pumps.
2.Description of the Prior Art
Gear pumps are used in a wide variety of fields. In pumps of this type two gearwheels usually engage so that they always rotate in opposite directions when in operation. If the surfaces of the gearwheels are bounded by walls and if a first space is defined around the engaging gearwheels and a second space around the disengaging gearwheels, the suction effect starting in the first space and the pressure effect in the second space can be utilised to move a medium located in the spaces.
Gear pumps have the advantage of having only a few components and can therefore be manufactured relatively simply. For example, the pumps can be driven in a non-contact manner by way of a magnetic coupling which benefits the separation of the fluid to be moved from other machine components. Due to the generally present direct connection of the suction and pressure space with a certain by-pass cross-section area these pumps can be used without problems, particularly in areas in which process-related occlusions frequently occur in the fluid inlet and/or outlet pipes.
EP 0 147 562 A2 and DE 199 15 784 A1 disclose a gear pump in which two gearwheels borne on separate axles are inserted between a first and a third of a total of three plates of a pump body. The second plate located between the first and the third plate has recesses for the gearwheels as well as the suction and pressure space. The inlet to the suction space, and the outlet from the pressure space are also in the second plate. The gearwheels are fitted in a rotating manner on the axles designed as rigid pegs.
In the known pumps the bearing axles are made of a different material from the gearwheels. Whereas, for example, the gearwheels can be made of synthetic material, the bearing axles consist of much stronger materials such as metal or ceramic. The gearwheels are sprayed or pressed onto the relevant bearing axle if the bearing axles are to be rotatable. The slide bearing sleeves required in this case must in turn be made of a material which is softer than the bearing axles.
However, the known gear pumps are costly to manufacture. Spraying on requires an additional handling system which inserts the bearing axles into the spraying tool. A further operating stage is also required for the pressed on variant, which results in additional costs. The positioning tolerance of several components also has to taken into account.